Variation in magnetic susceptibility in the Bellingshausen Sea continental rise since the last glacial period and implications for terrigenous material input mechanisms

Abstract

Magnetic susceptibility (MS) is routinely used as a proxy for terrigenous material input to Antarctic continental margin sediments. Variations in terrigenous input on glacial-interglacial timescales in this setting are related to a range of environmental changes; including to the cryosphere, atmosphere, and hydrosphere. However, the exact environmental factors and depositional processes that control MS values in sedimentary cores from the Antarctic continental margin remains unresolved. Here, we explore in detail sedimentary physical characteristics and MS values of core BS17-GC01 collected from Bellingshausen Sea continental rise, to understand how depositional process have varied during the late Quaternary. We found that input of terrigenous material increased markedly during Marine Isotope Stages (MIS) 2 and 4, compared to deposition during the adjacent interstadial and Holocene times. Variation in the bulk MS values were associated with changes in grain size. Size specific mass-normalized MS measurements show the fine fraction (<16 μm) has the highest MS values, followed by the coarse silt fraction (16–63 μm). However, because coarse silt is the predominant grain size, the increased bulk MS during MIS 2 and 4 are mainly driven by changes in this fraction. We propose that the coarse silt with high bulk MS values observed in glacial sediments were transported to the site as iceberg rafted debris, originating from the Bellingshausen Sea shelf region. In contrast, grains >1 mm – a commonly applied proxy for glacial transport in this setting – were observed during MIS 1 and 3 only. We conclude these contrasting signatures of iceberg rafted debris in this Bellingshausen Sea core arise from changes in the to the erosive dynamics of the adjacent ice shelf and continental shelf on glacial/interglacial timescales. • The MS in the Bellingshausen Sea co-varied with Antarctic ice core dust record. • The correlations of MS and dust record can be used for obtaining chronological points. • The MS is controlled by source/transport mechanism changes resulting in grain size change. • MS increases during MIS 2 and 4 are ascribed to increased coarse silt having high MS. • The coarse silt fraction during glacial periods was transported by icebergs.